[rules-users] help, Unable to create Field Extractor for ....

I meet working a simple example to interiorize with jboss rules and I obtain the following error: Exception in thread "main" org.drools.rule.InvalidRulePackage: Unable to create Field Extractor for 'CantSegundos' : [Rule name=Valida Duracion nula, agendaGroup=MAIN, salience=0, no-loop=false] *org.drools.RuntimeDroolsException*: *org.drools.RuntimeDroolsException*: java.lang.NullPointerExceptionUnable to create Field Extractor for 'CantSegundos' : [Rule name=valida Duracion , agendaGroup=MAIN, salience=0, no-loop=false] * org.drools.RuntimeDroolsException*: *org.drools.RuntimeDroolsException*: * java.lang.NullPointerException * at org.drools.rule.Package.checkValidity(*Package.java:408*) at org.drools.common.AbstractRuleBase.addPackage(*AbstractRuleBase.java:288* ) at prototipo.Prueba.main(*Prueba.java:27*) the class main is: * public* *static* *final* *void* main(String[] args) *throws* Exception { * final* PackageBuilder builder = *new* PackageBuilder(); * *builder.addPackageFromDrl( *new* InputStreamReader( Prueba.* class*.getResourceAsStream( "regla.drl" ) ) ); * final* RuleBase ruleBase = RuleBaseFactory.*newRuleBase*(); * ruleBase*.addPackage( builder.getPackage() ); * final* StatefulSession session = ruleBase.newStatefulSession(); * *Integer segundos = *new* Integer(5); * *validaciones valida = *new* validaciones(); * *valida.setCantSegundos(segundos); * *session.insert( valida); * *session.fireAllRules(); *in the rules is:* * package prototipo import prototipo.validaciones; rule "Valida Duracion nula" when v : validaciones(CantSegundos == 0) then v.setResultado("I"); System.out.println( "obtenemos" + v.getResultado() ); end rule "valida Duracion "when v : validaciones(CantSegundos > 0) then v.setResultado("S"); System.out.println( "obtenemos" + v.getResultado()); end ** Thank you for helping me. *** **